One type of optical modulator that has promise for high-speed applications such as exascale computing and next generation optical communications is the resonant optical modulator. A resonant optical modulator includes an optical resonator that is typically a waveguiding ring or disk of silicon, although other geometries and other materials are not excluded. An input and output optical beam is coupled to the resonator by directing the beam through a waveguide, which may e.g. be a rectilinear planar waveguide, situated within an evanescent coupling distance of the resonator.
Within a characteristic wavelength band, such a modulator is relatively transmissive when light coupled into the modulator excites a resonant mode of the resonator, and is less transmissive when it goes out of resonance with the coupled light. The resonance may be controlled by, e.g., thermal or electronic modification of the optical velocity within the resonator.
One of the advantages of resonant modulators relative to competing technologies is that they occupy a relatively small volume, and as a consequence are conservative as to wafer real estate and as to power demands. One of the challenges in the area of resonant modulators is to maintain the advantage of small volume, while accommodating such features as heaters for thermal tuning, and such signal isolation as is necessary in order to accommodate differentially driven modulation signals.